The battle to become Oxford professor of poetry in 2009 was worthy of a mock-heroic poem by Alexander Pope. First, the frontrunner Derek Walcott pulled out following a smear campaign that disinterred allegations of sexual harassment dating back to the 1980s and 90s. Then the eventual victor, Ruth Padel, had to resign after less than a fortnight, when she was implicated in the smear. It was an ugly business, but it did get poetry – that most marginalised of literary forms – on to the front pages for a while.

There was also a less well-publicised by-product. When Walcott withdrew, Essex University decided to reintroduce its own professorship of poetry, a post once grand enough for Robert Lowell, and offer it to Walcott. So instead of delivering dense lectures among dreaming spires, he spends a fortnight each year teaching and giving readings amid brutalist tower blocks – and excavating a less well-known part of his oeuvre, his plays.

This week, at the university's Lakeside theatre, he is directing Pantomime, his 1978 comic two-hander. This explores the tensions of post-colonial Tobago through the character of washed-up English actor Harry Trewe, who has bought a clapped-out guesthouse on the island, and galvanic local Jackson Phillip; having abandoned his career as a calypso singer, Jackson is now a waiter at the guesthouse. Harry wants to put on a pantomime, based on Robinson Crusoe, and is keen for Jackson to take part. The story of Crusoe – the archetypal imperialist, a plantation owner who is shipwrecked while bringing slaves from Africa – is fertile ground for an examination of race and identity in the Caribbean after the tide of empire had gone out. Who should play Crusoe and who Friday? Who is really in charge on the island now?

At the Lakeside, Walcott sits in the front row, wearing jeans, striped braces and a bright red baseball cap, watching rehearsals. It is unlikely attire for a Nobel laureate, but then he is not your average literary grandee. Revering English literature since his boyhood in Saint Lucia, he takes his work seriously, himself less so. "What the fuck is wrong with me?" he says, as he forgets the sequence of events in the play. As a director, he prefers to watch and listen, rather than lay down the law. "There's something terrific happening here," he says at one point, though it's for the actors to discover what.

We talk during a break. Walcott is accommodating, yet you are never quite at ease. At 82, a little deaf and forgetful, he has no time for foolishness. He thinks my first question – can a play written 30 years ago still say something about the coloniser and colonised? – foolish. "That's a hell of a thing to ask me," he says, his voice rising with a lovely, growly West Indian lilt. "I would imagine that a play might last. If it's any good, it lasts."

He wrote Pantomime in a matter of days, the words tumbling out so fast he dictated rather than wrote much of the dialogue. "I was playing the two roles myself," he says. His two grandfathers were white, his grandmothers black, so he can identify with both sides. But he warns against seeing Pantomime only in political terms. "The surface of the play looks like a cliche: a situation between a black guy and a white guy. But what I wanted to talk about more was the relationship between two artists from different cultures – basically the same kind of person, one working in music hall, the other in calypso. There's an affinity between them."

He doesn't, however, entirely disclaim the politics. "In terms of racial relationships in the Caribbean, you still have a tourist economy in which people are asked to behave in a certain way. It's become very emphatic now, the idea of service. But you have to be careful it doesn't turn into slavery: the insistence that you must smile and serve for the sake of the island. Advertisements that have everybody grinning and insisting you have to make people happy, that's our job in life. That's dangerous. It's even worse that it's black people – the tourist board, the government – doing it to themselves."

Walcott has written more than 20 plays. Why are they so little known? "I am not defined as a black writer in the Caribbean," he says, "but as soon as I go to America or the UK, my place becomes black theatre. It's a little ridiculous. The division of black theatre and white theatre still goes on, and I don't wish to be a part of any one of those definitions. I'm a Caribbean writer." The essence of the Caribbean, he says, is multiracialism. "On my street, it could be an Indian, a Chinese, a Lebanese, all living together. Whether happily or not doesn't matter."

Walcott says he should not be seen as a pioneer of Caribbean art: he built on the achievements of writers who preceded him. Many left to make their careers elsewhere, but Walcott chose to stay. "I made a vow that I wouldn't be tempted by what could happen to me if I went to Europe. I thought, 'You could be absorbed in it – it's so seductive, you might lose your own search for identity.' Then, when I did finally go to Europe, I was able to resist it because I had established my own identity." Did that commitment to the Caribbean delay acceptance of him? "English reviewing was very patronising," he says. "There were categories for Commonwealth writing. What is a Commonwealth writer? Is he less than somebody who's in the capital? I was infuriated by the semi-contempt in which Commonwealth writing was held."

Despite being patronised, Walcott showed remarkable confidence, self-publishing his first book of poems at 19. "I knew exactly where I was and what I was doing," he says. "My father [who died when Walcott was one] used to write. My mother taught Shakespeare and used to act. So I had that atmosphere at home. I knew very early what I wanted to do and I considered myself lucky to know that's what I wanted, even in a place like Saint Lucia where there was no publishing house and no theatre." That throwaway line emphasises the extent of his achievement, won by talent and a ferocious work ethic.

In the 1960s and 70s, Walcott was not just patronised by much of the white establishment, but attacked by some black critics for having sold out because he used traditional literary forms. "I went through a lot of crap. People criticising you for being Afro-Saxon, but the point was that they were criticising me in English. Why were they doing it in English? Why weren't they doing it in whatever language they wanted to invent?"

He says his relationship with English literature and culture is that of a detached admirer. "When I come to England, I don't claim England, I don't own it. I feel a great kinship because of the literature and the landscape. I have great affection for Edward Thomas and Philip Larkin, but there's still this distance: looking on at what I'm admiring, separate from what I am. And that's OK. That makes for drama of a kind, and a more careful introspection about what you're liking and why."

Walcott has had a long-running feud with his fellow Nobel laureate VS Naipaul, who left his native Trinidad and has been critical of the poverty of indigenous culture. Walcott made a fierce public attack on Naipaul in 2008, in a poem called The Mongoose: "I have been bitten, I must avoid infection/ Or else I will be as dead as Naipaul's fiction." Walcott claims Naipaul has misrepresented Trinidadian culture. "It's very upsetting," he says, "because people were defenceless. He could call them whatever he wanted, in very elegant English. He should not have used his talent to abuse his own people. I wanted to help him recognise that."

Walcott's breakthrough book was Omeros, his 1990 reworking of The Odyssey set in Saint Lucia. "The girl who typed it was saying, 'This is going to win the Nobel prize.'" She was right, but he insists he never thought in such terms. "It's startling to me when somebody says, 'Your form is classical.' I know what's inside me. I know what I enjoy. It's nothing to do with what I'm described as being – it's a contradiction of that almost. My delight in things is definitely Caribbean. It has to do with landscape and food. The fact that my language may have a metrical direction is because that's the shape of the language. I didn't make that shape."

And the Oxford professorship? How badly burned did he feel? "I don't think ultimately I wanted the job," he says. "It would have been too much work. I'm not a good scholar. Like [Walt] Whitman, I contradict myself very quickly, and you can't have an academic who does that." Why did he withdraw from the election? "I felt if I was disgracing people, I'd better get out of there." In any case, he says, "being in the Caribbean and being professor of poetry at Oxford was a contradiction." Which is why, in the end, the only way was Essex.